A typical internal combustion engine in a motor vehicle operates by combusting a mixture of a vaporized fuel (i.e. gasoline) and air in a cylinder or combustion chamber. Generally, the combustion chamber includes a piston that is forced to translate or move up and down as a result of the combustion of the fuel/air mixture. The piston is rotatably secured to a crankshaft. The movement of the piston rotates the crankshaft which ultimately rotates the drive wheels of the vehicle.
Many internal combustion engines have four-stages of operation. These stages, also referred to as strokes, relate to the position of the piston within the combustion chamber. For example, a typical four-stage operation includes an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. During each stroke the piston moves from one end of the combustion chamber to the other end of the chamber and the crankshaft rotates 180 degrees. During the intake stroke the fuel mixture is drawn into the combustion chamber. During the compression stroke the fuel mixture is compressed and then ignited. During the expansion stroke the piston is forced toward the bottom of the combustion chamber by the combustion process. Finally, during the exhaust stroke the combustion gases are expelled from the combustion chamber.
Fuel is delivered to the combustion chamber using a fuel delivery system. Conventional fuel delivery systems include, for example, a fuel tank, a low pressure pump, a high pressure pump, a plurality of fuel lines, a fuel rail, a pressure sensor, and a fuel injector. The low pressure fuel pump pumps the fuel out of the fuel tank and pressurizes the fuel to a first pressure. The low pressure pump is typically electrically driven by the vehicle's battery. The high pressure pump pumps the fuel into the fuel rail at a second pressure that is higher than the first pressure. The high pressure pump is typically mechanically driven by the engine. The pressure sensor transmits a signal indicative of the pressure sensed in the fuel rail to a control device, such as a microcontroller. The fuel rail distributes the fuel to the fuel injectors which inject fuel into the cylinders of the engine.
Conventional fuel delivery systems inject fuel into the combustion chamber during the intake stroke and during the compression stroke. However, this method of injection is not sufficient to supply the required amount of fuel to the fuel injector during certain engine operating conditions, such as a cold start condition. This may result from, for instance, the pressure in the fuel rail being insufficient during the cold start condition because the high pressure fuel pump is unable to supply the necessary flow. This typically occurs because the engine is operating at a low speed during the cold start condition prior to reaching a steady state condition. As such, vehicles started under a cold start condition generally need more fuel than what the high pressure fuel pump is capable of delivering due to the low operating speed of the engine. Accordingly, during cold start conditions these engines mostly rely on the low pressure fuel pump.
Therefore, there is a need for an improved system and method for delivering fuel to a direct injection engine to overcome the limitations of the conventional fuel delivery system during, for example, cold start conditions.